SIP phone extension for Mozilla Thunderbird

What is Cockatoo?
Cockatoo is a project about implementing SIP/SIMPLE as an extension for Thunderbird (XPCOM component/XUL interface) that enables users to phone contacts and see their presence state.
Cockatoo is implemented by Filip Dalüge as part of Google's Summer of Code. It is mentored by Brian King of MozDev and makes use of the Zap SIP stack.
Details
Users shall be able to do a phone call by one click out of their address book and to reply to emails by phone call. To put this into practice, the open standards SIP, SDP, RTP as well as audio codecs have to be implemented. These functionalities will be included into Thunderbird as an XPCOM component.
On top of this component, an XUL interface will be set up that does several tasks:
- Creating a basic standalone interface for accessing URIs of type tel and sip. These can be accessed by entering it directly or choosing an address from an address book sidebar.
- Including a field "SIP address" to Thunderbird's address book cards. Email addresses will be mapped to corresponding SIP addresses so that a sender of an email with a known SIP address can be contacted directly.
- Displaying the presence state of email senders using the SUBSCRIBE/NOTIFY extensions of SIP defined in RFC 3856. Any other SIMPLE services like MESSAGE (defined in RFC 3428) should be implemented at a later time.
- Enabling the user to call persons from several interfaces of Mozilla Thunderbird like the address book or recieved emails if there is a known sender.
Motivation
SIP is the most used open standard for telecommunication over IP, it is standarized by RFC 3261. As more and more devices like notebooks carry microphones and a permanent internet connection with them (WLAN), it is to be expected that users will want to use their existing environment for phoning as well.
Especially the last mentioned feature (calling by click using the address book) is an extremely useful capability, as address books of many Thunderbird users already contain phone numbers. These ordinary phone numbers can be called over a SIP provider's gateway.